Defrosting device for refrigeration unit



March 1967 JUICHI HONDA DEFROSTING DEVICE FOR REFRIGERATION UNIT FiledMay 21, 1965 F IG.

5 F/GZ TTORNEY United States Patent 3,310,956 DEFROSTING DEVICE FORREFRIGERATKGN UNIT Juichi Honda, 482-2 Tomita, ()hiracho,Schimotsnga-gun, Tochigi-ken, Japan Filed May 21, 1965, Ser. No. 457,7128 Claims. (Cl. 62-196) This invention relates to defrosting devices forrefrigerating units such as cold storages and freezers and involves animprovement in defrosting devices of the type in which hot refrigerantgas from the compressor is fed into the evaporator of the refrigeratingunit.

In general, this hot gas type of deforsting device necessitates, inaddition to the refrigerating unit including a motor-driven compressorcondenser, capillary tube and evaporator, at least such devices as asolenoid valve as sembly (A) for changing the path of hot gas, a switch(B) capable of continuously sensing the evaporator temperture to detecta certain frost temperature appropriate for defrosting operation and acertain deforst temperature at which such operation is to be completed,another switch (C) for manually or automatically starting the defrostingoperation, and appropriate wiring connections between these elements A,B and C.

The hot gas type defrosting device in its early stages of developmentincluded a series connection of the elements A, B and C, which wasarranged in parallel to the compressor circuit. The switch device Cemployed to start the defrosting operation was one operable manually orautomatically to close the associated circuit and also manually orautomatically to open the same. Thus, with this early type of defroster,the switch C for starting the defrosting operation is closed when theswitch B detecting the frost temperature appropriate for the defrostingoperation is closed. The closing of switch C causes the solenoid valveto operate to rush hot refrigerant gas from the compressor into theevaporator thereby starting the defrosting operation. Upon completion ofthe defrosting operation, the switch B detecting the evaporatortemperature is rendered inoperative and accordingly the switch C isopened to stop conveying hot refrigerant gas to the evaporator.

With the above-described defrosting device, the switch B is arranged toclose the associated circuit upon detection of the evaporatortemperature appropriate for the defrosting operation. Strictly speaking,however, of this circuit-closing operation of switch B, the time when itis operatively closed is not always appropriate to start the defrostingoperation. In other words, the switch B is always closed when theevaporator temperature is reduced to a certain frost temperature, suchas an extreme low level in general ranging from l C. to 20 C., theevaporator is in a state to be defrosted carrying a substantial amountof frost thereon. For example, however, in case the system is operatedfor rapid cooling immediately after the desired defrosting has beencompleted, the evaporator temperature may reach an extreme low levelbecause of such rapid cooling to cause closing of the circuit even if nofrost is found on the evaporator. Thus, with this defrosting device, ifthe user fails to open the switch C after the defrosting operation andthe evaporator temperature is reduced by any immediate rapid coolingoperation of the system, the switch B may possibly be closed again tosend hot gas into the evaporator.

One improvement previously made in this type of defroster in an effortto overcome the above deficiency is as follows: For one switch means areprovided a diaphragm means for detecting the temperature of theevaporator when completely defrosted and imparting to the switch only amotion in the opening direction and a pushbutton means for imparting tothe switch a motion ice primarily in the closing direction. Further, theswitch includes a leaf spring or like biasing means and, once actuatedby the diaphragm or push-button means, the switch can never be restoredunless it is acted upon by some external force. The above threecomponents are normally brought together in a casing to form an integraldevice, generally called defrosting thermostat, which is used incombination with an appropriate solenoid valve assembly. Thisarrangement apparently includes a single switch which is closed by thepushbutton to start the defrosting and opened when the evaporatortemperature reaches a defrost temperature at which all the frostproduced on the evaporator has been defrosted. It is noted that, afterthe switch has been opened 'or restored automatically in response to theevaporator temperature, there is no possibility that hot gas beunnecessarily fed into the evaporator unless the user intentionallyoperates to restart defrosting.

It is also noted, however, that such defrosting thermostat usable with adefrosting device of the type described should have a physical force inresponse to the rise and fall of the evaporator temperature. Thediaphragm device achieves this purpose. The diaphragm device, however,is itself complicated in structure and function and liable tomisoperate. Moreover, the defrosting thermostat includes a pushbuttonmeans and a switch in addition to the diaphragm device, as describedhereinbefore, and the three components must be combined to work incoordination. It follows, therefore, that the defrosting deviceutilizing such thermostat is deficient in that it is complicated inconstruction just because of its incorporating the thermostat and is notfully reliable in function. Apparently, the same can be said even if atimer instead of the pushbutton means is used for automatically closingthe switch.

Also, the defrosting thermostat described is usually arranged in theinsulation wall of the refrigerator unit to save space and foroperational reasons. Such thermostat arrangement in the insulation isevidently undesirable from the viewpoint of the insulation efiiciency ofthe re frigerator walling. In addition, recent use of polyurethane foamin refrigerator units has realized reduction in thickness of theirinsulation walls owing to the excellent insulating property of thematerial, and it is practically impossible to arrange a defrostingthermostat of the type described in the insulation wall ofsuch reducedthickness.

Accordingly, there is an increasing demand for a defrosting device whichis designed not to feed any hot gas needlessly into the evaporator afterthe end of the defrosting operation, is simple in structure and reliablein function, and can be installed in any desired location within therefrigerator unit.

The present invention is intended to provide an improved defrostingdevice which meets the above demand with success.

As to a solenoid valve assembly, it is well known that it includes asolenoid coil, an armature or plunger and a needle element carried bythe armature for opening the bypass conduit to convey hot refrigerantgas to the evaporator. The intensity of magnetic force produced by thesolenoid coil which is required to actuate the plunger or armature tothe actuated position thereof for opening and closing the associated gaspassage, differs in magnitude from that required to hold the armature inits actuated position, i.e., the latter is more or less smaller than theformer. The present invention is principally based upon this fact andforms its ingenious application to the defrosting art.

More specifically, the present invention is characterized in that itincludes a solenoid valve assembly so designed that the solenoid coilproduces, upon closing of a bimetal switch provided for detection of theevaporator temperature appropriate to start defrosting, a magnetic forceof an intensity insuflicient to eifectively actuate the armature butsufiicient to hold the armature in its actuated position, andsubsequently produces a magnetic force of an intensity suflicient toeffectively actuate the armature for a short period of time to open thebypass passage for directing hot gas into the evaporator.

The above and other objects and features of this invention will becomemore apparent by reference to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of one embodiment of the invention;

FIG. 2 is a sectional view of the solenoid valve assembly used in theembodiment shown in FIG. 4;

FIG. 3 is a circuit diagram illustrating another embodiment of theinvention;

FIG. 4 is a circuit diagram of a further embodiment of the invention;and

FIG. 5 is a cross section of the solenoid valve assembly used in FIG. 4.

Referring to the drawings, reference numeral 1 indicates a compressor; 2a condenser; 3 a capillary tube; and 4 an evaporator. These fourcomponents are in fluid communication with each other through conduitlines 5a, 5b, 5c, 5d and 5e, as illustrated, to form a refrigeratorunit. Thus, the high-temperature high-pressure gaseous refrigerant inthe compressor 1 enters the condenser 2, in which the gas releases heatcontained therein and then it is liquefied. The liquefied refrigerant isreduced in pressure by passing through the capillary tube 3 and is thenvaporized in the evaporator 4 to return to the compressor 1 in gaseousform. As is Well known, the liquid refrigerant takes in heat from theenvironment when it is vaporized, and a refrigerator includes anevaporator for vaporization of liquid refrigerent and arranged in aheat-insulated chamber for the purpose of cooling its interior.

Reference numeral 6 indicates a solenoid valve assembly schematicallyshown in FIG. 1 with a bypass conduit 7 connected at one end thereofwith the solenoid valve assembly and at the other end thereof with theupstream side of the evaporator.

Referring to FIG. 2, which illustrates the details of the solenoid valveassembly, the valve body or casing 8 is formed in its lower portion witha cavity 9 and includes a tubular guide portion 19 which extendsvertically upwardly. Formed in the valve casing 3 on its opposite sidesare apertures 14a and 14b which communicate with the cavity 9. Alsoformed in the valve casing 8 at its bottom is an aperture 14C whichcommunicates with the cavity 9 and is opposite to the bottom end of thehollow 13 in the tubular guide portion 19. As shown, these apertures14a, 14b and Ida fixedly receive conduits 5a, 5b and 7, respectively.The tubular guide portion of the valve casing 8 is covered at its opentop by a cap 15, which tightly closes the hollow space 13 in the guideportion and the cavity 9 in the casing body.

A solenoid coil 16 is arranged about the periphery of the tubular guideportion 143 for producing a desired magnetic force when energized. Thesolenoid coil 16 includes a large number of turns of a wire wound aboutthe cylindrical wall 13 of a hollow toroidal bobbin 17, which is made ofan electrically insulating material and includes in addition to thecylindrical wall 18 circular flange walls 19 and 20 extending radiallyoutwardly from the cylindrical wall 18 at its top and bottom. Obviously,the solenoid coil has two terminals, not shown in FIG. 2. An iron yoke21 is provided to wrap the solenoid coil 16 for the purpose of makinguniform the distribution of the lines of magnetic force formed by thesolenoid coil 16. The coil 16 and yoke 21 are assembled together intoroidal shape, as apparent in FIG. 2, and the tubular guide portion 10of the valve body 8 extends upwardly through the central bore of suchassembly. A disc spring 22 secures the coil and yoke assembly to theshoulder portion of the valve casing 8.

A hollow plunger or armature 23 has an outside diameter more or lesssmaller than the inner diameter of the tubular guide portion 10 and isloosely fitted in the hollow 13 of the tubular guide portion 10 definingtogether with its inner wall 12 a small space therebetween for verticalmovement. Thus, when actuated by the solenoid coil, the armature 23 isattracted upwardly. The hollow armature 23 has on its inner wall 24 atthe bottom thereof a radially inwardly extending annular restrainingflange 25. A needle element 26 has an upper stern portion loosely fittedto the central aperture of the annular flange 25 on the hollow armatureand extended into the interior of the armature and has an annular flange27 at the top of the stem portion in the interior of the hollow armature23 in axially opposite relation to said restraining flange 25. As thearmature 23 rises, the flanges 25 is brought into engagement with flange27, so that the needle element 26 is raised together with the armature23. The needle element 26 has a body portion conically shaped at thebottom thereof to form a sharp needle point and formed fiat at the topthereof to form annular shoulder 29. When the armature is renderedinoperative, the armature 23 is supported on the needle element 26 withits annular shoulder 29 in abutting engagement with the bottom of thearmature 23. As shown, the needle element 26 is disposed opposite to theaperture 140, formed in the bottom of the valve casing 8, and normally,or when the element 26 is free from any external influence, its sharpbottom end is fitted in the aperture to completely close it at itsconstricted top end 3-0.

In the aforedes-cribed refrigerationcycle, the solenoid valve 6 duringcooling operation is in the state shown in FIG. 2 with its needleelement 26 positioned to close the bypass conduit 7 so that hot gasflowing from the compressor 1 through conduit 5a is allowed to enterconduit 51). For defrosting the evaporator 4, the solenoid coil 16 isenergized to actuate the armature 23 so that the latter is raisedcarrying the needle element 26 to open the aperture 140. As aconsequence, hot gas from the conduit 5a proceeds into the bypassconduit 7 owing to the pressure difference between the conduits 5a and5b. The hot gas is effective to defrost the evaporator 4 by passingthrough conduit 5a.

In the embodiment as described in FIG. 1, a bimetal switch 33, which isrendered operative in accordance with the evaporator temperature, isconnected in series with a resistor 34 and a break switch 35 operativelyopened. This series connection is connected in parallel with a switch32.

The solenoid coil 16 of the solenoid valve assembly 6 is connected inseries with the parallel connection of the bimetal switch 33 and theswitch 32 to an electric power source 31. According to the presentinvention, the switch 32 is designed to close for a period of time notlonger than that required to defrost the evaporator 4 but sufficientsuch that the solenoid coil may completely actuate the armature eithermanually or automatically, for example by an electric timer or bycounting the number of refrigerator door openings.

In practice, the switch may include an externally arranged pushbuttonwhich, when depressed, is arranged to actuate the solenoid coil.

In case the evaporator temperature falls, the switch 33 is closed whenthe temperature reaches a level appropriate for defrosting, which isbetween -15 C. and -20 C. On the other hand, in case the evaporatortemperature rises as the defrosting proceeds, the bimetal switch 33 isopened when the evaporator has been completely defrosted, or atapproximately 4 C. A resistor 34 is connected in the bimetal switchcircuit 33a. Otherwise, when the bimetal switch 33 is closed, thesolenoid coil 16 would be energized by the full current flowing throughthe circuit 16a to produce a substantially large magnetic forceeffective to actuate the armature 23. It would follow, therefore, thatthe armature 23 be actuated to open the bypass conduit 7 each time thebimetal switch 33 is closed. This is obviously undesirable and can beprevented by the insertion of the resistor 34 in the bimetal switchcircuit 33a. According to this invention, such resistor is specificallyselected to limit current flow through the circuit 33a and solenoid coilcircuit 16a so that only a magnetic force is produced by the solenoidcoil 16 with an intensity which is insufiicient to actuate the armature23 but sufiicient to hold the armature at the actuated position thereofonce it is actuated. Thus, the resistor 34 should be designed, by takingthe number of turns of the solenoid coil 16 and the size of armature 23into account, to limit the current flow through the solenoid coil sothat only a magnetic field is produced with the predescribed intensity.

The following is a description of the defrosting operation of theembodiment described in FIG. 1.

When no frost is found on the evaporator 4, there is no current flowthrough the bimetal switch circuit 330 or solenoid coil circuit 16a.During use of the refrigerator unit, as frost is formed on theevaporator in an increasing amount, the temperature of the evaporator isreduced and reaches a level of from l5 C. to 20 C., accordingly thebimetal switch 33 is closed to cause an electric current flow throughthe solenoid coil circuit 16a by way of bimetal switch circuit 33a. Thecurrent is limited by the resistor 34, as described hereinbefore, sothat the magnetic force produced by the solenoid coil 16 is notsufiicient to actuate the armature 23 to any effective extent and nodefrosting occurs. For defrosting operation, it is only necessary forthe user to close the switch 32 to render the solenoid coil operativewhen the user, observing the frosted state of the evaporator, feels theneed of it being defrosted. In this manner, the solenoid coil circuit16a is fed with a full current flowing directly from the power source31, but not by way of the bimetal switch circuit 33a, with the resultthat a substantial magnetic force is formed in the solenoid coil 16. Themagnetic force is effective to actuate the armature 23 verticallyupwardly within the tubular guide portion 10 of the valve casing 8.Thus, the armature 23 carries with it the needle element 26 verticallyupward to open the bypass conduit 7. Consequently, hot gas from thecompressor 1 is allowed to fiow through conduit 5a into bypass 7 toeffect defrosting of the evaporator.

It is to be noted here that the switch 32 is designed to operate for alimited period of time independently of the other defroster components.Namely, the switch acts to reopen the solenoid coil circuit shortlyafter the armature 23 has been completely actuated and thus acts toclose the circuit for the sole purpose of actuating the armature. Afterthe opening of the solenoid coil circuit 16:: including switch 32, thesolenoid coil is fed with a reduced cur-rent by way of the bimetalswitch circuit 33a to hold the armature 23 in its actuated position.This means that the defrosting operation is continued even after theopening of switch 32. After the evaporator 4 has been defrostedcompletely with its temperature raised, the bimetal switch 33 is alsoopened and thus all the circuits are de-energized. As the result, thearmature 23 and needle element 26 of the solenoid valve assembly 6 arerestored to their normal position closing the bypass conduit 7 tocomplete the defrosting cycle.

During defrosting, if it is desired to stop the defrosting operation, itis only required to open the switch 35 temporarily. By doing this, thearmature 23 is restored from its activated position to its normal one toclose the bypass conduit 7 and the flow or hot gas to the evaporator 4is interrupted.

In the above-described embodiment, the series connection of the bimetalswitch 33 and resistor 34 is connected in parallel to the switch 32.Apparently, however another arrangement is that the resistor 34 alone isconnected in parallel with switch 32 and arranging the bimetal switch 33and the solenoid coil are connected in series therewith, as illustratedin FIG. 3 is also operable in this invention.

FIGS. 4 and 5 illustrate another embodiment of the present invention. Asshown, this embodiment employs a solenoid coil means 16, which includesdouble wound primary and a secondary solenoid coils 36 and 37,respectively. The primary coil 36 together with bimetal switch 33 andswitch 35 is connected to a power source 31 in series while thesecondary coil 37 is connected to the same together with the switch 32,the two coils being in parallel with each other. One example of thesolenoid valve assembly employing such double-wound solenoid means isshown in FIG. 4, which illustrates a primary coil 36 wound about asecondary coil 37.

The number of turns of the primary and secondary solenoid coils isspecified as follows. Namely, the primary coil 36 includes a number ofturns which produces a magneticforce of an intensity insufficient toactuate the armature 23, which carries needle element 26 for opening butclosing the bypass conduit, and sufficient to hold the armature in itsactuated position while the secondary coil 37 includes a number of turnswhich produces a magnetic force with an intensity which is by itself or,when combined with the field intensity caused by the primary coil 36,effective to actuate the armature 23.

The defrosting operation of this embodiment is as follows.

As long as no frost is found on the evaporator 4, there occurs nocurrent through the primary or secondary solenoid coil circuits 36a or37a. As frost is formed on the evaporator in an increasing amount, itstemperature is reduced, and, when it reaches a level of from -l5 C. to20 C., the bimetal switch 33 is closed to energize the primary solenoidcoil 36, which produces a magnetic force with intensity which isinsufficient to actuate the armature 23 for starting defrosting. On thisoccasion, if defrosting is required, it is only necessary to close theswitch 32 so that in addition to the primary solenoid coil 36, thesecondary solenoid coil 37 is energized and now both the primary andsecondary solenoid coils 36 and 37 produce a magnetic force. Themagnetic force formed by the secondary solenoid coil 37 alone orcombined with the force formed by the primary solenoid coil 36 issuflicient to effectively actuate the armature 23 and start defrosting.Obviously, the switch 32 is arranged to be operated independently of theother defroster components to close the circuit for a short period oftime, as described hereinbefore, and the armature 23 is actuated whenthe switch 32 and the bimetal switch 33 are closed and is held in itsactuated position by the primary solenoid coil 36 after the switch 32 isopened. The defrosting operation is completed when the bimetal switch,sensing the evaporator temperature, opens.

With this embodiment, it is possible to indicate whether the defrostingis being effected or not by a paralled connection of an electric lamp 38with the secondary solenoid coil 37 (FIG. 4). The lamp 38 is firstlighted by closing the switch 32 and subsequently by the electromotiveforce induced in the secondary solenoid coil 37 by energization of theprimary one,

As apparent from the foregoing description, the switch 32, whenoperative renders the solenoid coil operable to actuate an armaturecarrying a needle element provided in the bypass conduit, is onlyrequired to render the solenoid coil operable for a short period oftime, and thus is of the type operable independently of the otherdefroster components to close for a short period of time. This switch isobviously in its open position when any switch operable in response tothe evaporator temperature is again rendered operative during normalrefrigerating operation just after completion of the defrostingoperation, and thus effectively eliminates the danger of the armaturebeing actuated again for defrosting operation.

Also, since the switch provided for actuation of the armature to startdefrosting is of the type operable independently of the other defrostercomponents, as described hereinbefore, there is no need of employing anymeans for mechanically transmitting the change of the evaporatortemperature to the switch. Thus, a bimetal switch may be used just formeans directly responding to the evaporator temperature and thus anydiaphragm device conventionally used in the defroster of the characterdescribed can be dispensed with, eliminating any labor and costpreviously required to assemble such defroster elements as the diaphragmdevice, switch and pushbutton means. Thus, according to the presentinvention, a defrosting device is provided which as a whole issimplitied in structure and function and reliable in operation.

In addition, the defrosting device according to the present inventiondoes not necessitate any thermostat which is relatively voluminous andhas only a limited freedom of location, and thus has no adverse effectupon the insulation efliciency of the refrigerator walling and, with thesolenoid valve, switch for starting the defrosting operation, bimetalswitch and other components connected by wiring, can be installed freelyat any location.

Although a few embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart and various changes and modifications may be made therein Withoutdeparting from the spirit of the invention or from the scope of theappended claims.

What is claimed is:

1. A defrosting device in combination with a refrigerating unitincluding a compressor, condenser, capillary tube and evaporator influid communication, comprising bimetai switch means operatively closedin response to the temperature of the evaporator of the refrigeratingunit, a solenoid valve assembly connected with said compressor, a bypassconduit connected at one end thereof to said solenoid valve assembly andat the other end thereof to the upstream side of the evaporator; saidsolenoid valve assembly including a solenoid coil associated with saidbimetal switch means, an armature arranged in said solenoid coil andreciprocably moved by said solenoid coil, a needle element carried bysaid armature for operatively opening and closing said bypass conduit,said solenoid valve assembly being designed to produce when said bimetalswitch means is closed a magnetic force with an intensity insufficientto actuate said armature and sufficient to hold the armature in anactuated position; and switch means associated with said solenoid coiland independently rendering said solenoid coil operable to produce anadditional magnetic force suflicient to actuate the armature in saidsolenoid coil.

2. A defrosting device according to claim 1, which further comprises aresistor element connected in series with said bimetalswitch means, theseries connection of said resistor element and said bimetal switch meansbeing connected in parallel with said switch means, and the parallelconnection of said series connection and said switch means beingconnected in series with said solenoid coil to an electric power sourcefor energizing said solenoid coil.

3. A defrosting device according to claim 2, which further comprisessecond switch means inserted in series in the series connection of saidresistor element and said bimetal switch means, said second switch meansrendering said solenoid coil inoperative such that said armature closessaid bypass conduit.

4. A defrosting device in combination with a refrigerating unitincluding a compressor, condenser, capillary tube and evaporator influid communication, comprising a solenoid valve assembly connected withsaid compressor and including a solenoid coil, an armature axiallymovably positioned in said solenoid coil, a needle element carried bysaid armature, a bypass conduit connected at one end thereof to saidsolenoid valve assembly and at the other end thereof to the upstreamside of the evaporator, said needle element opening and closing saidbypass conduit in response to the movement of said armature, bimetalswitch means activated in response to the temperature of the evaporator,a resistor element connected in series with said solenoid coil to anelectric power source, said solenoid coil producing upon closing of thebimetal switch means, a magnetic force with an intensity insufficient toactuate said armature and sufficient to hold the armature in an actuatedposition, and a switch means connected in parallel with said resistorelement for bypassing the resistor element and independently causingsaid solenoid coil to produce an additional magnetic force to actuatesaid armature.

5. A defrosting device according to claim 4, which further comprisessecond switch means connected in series with said resistor element inthe parallel connection of said resistor element and said firstmentioned switch means, said second switch means rendering said solenoidcoil inperative such that said armature closes said bypass conduit.

6. A defrosting device in combination with a refrigerating unitincluding compressor, condenser, capillary tube and evaporator in fluidcommunication, comprising a solenoid valve assembly connected with thehot gas outlet of said compressor, a bypass conduit connected at one endthereof to said solenoid valve assembly and at the other end thereof tothe upstream side of the evaporator, said solenoid coil means valveassembly including solenoid coil means, and armature axiallyreciprocab-ly movable within said solenoid valve assembly, a needleelement carried by said armature and for opening and closing said bypassconduit, said solenoid coil means including a primary solenoid coil toproduce a magnetic force with an intensity insufficient to actuate saidarmature and suflicient to hold the armature in its actuated positionand a secondary solenoid coil to produce an additional magnetic forcewith an intensity at least sufficient to actuate said armature, bimetalswitch means connected in series with said primary solenoid coil, andresponsive to the temperature of the evaporator, and independentlyoperable switch means connected in series with said secondary solenoidcoil to cause said secondary coil to activate said armature.

7. A defrosting device in combination with a refrigerating unitincluding compressor, condenser, capillary tube and evaporator in fluidcommunication, comprising:

a bypass conduit for bypassing said condenser and said capillary tubefor conveying hot refrigerant gas from said compressor to the upstreamside of said evaporator,

a solenoid valve assembly including a solenoid coil, an armatureactuated by said solenoid coil and a valve element carried by saidarmature for opening said bypass conduit when said armature is actuated,

bimetal switch means for sensing the temperature of said evaporator suchthat when the evaporator temperature drops under a predetermined frosttemperature said bimetal switch means closes until the evaporatortemperature exceeds another predetermined defrost temperature, andswitch means for operating independently of said bi-metal switch meansat least for a period of time sufficient for completion of the actuationof said armature,

said solenoid coil being provided to produce a magnetic force with anintensity insufficient to actuate said armature but suflicient to holdthe armature at the actuated position thereof when said solenoid coil isenergized by the bimetal switch means and with another intensitysufflcient to actuate said armature when said solenoid coil is energizedby both the switch means and the bimetal switch means whereby the bypassconduit remains opened independently of the op- 9 eration of said switchmeans as long as said bimetal switch means remains operative when boththe bimetal switch means and the switch means have been previouslyactivated.

8. A defrosting device according to claim 7, which further comp-risessecond switch means for deactivating the solenoid coil to release thearmature and enable the valve element to close the bypass conduit.

References Cited by the Examiner UNITED STATES PATENTS MEYER PERLIN,Primary Examiner.

1. A DEFROSTING DEVICE IN COMBINATION WITH A REFRIGERATING UNITINCLUDING A COMPRESSOR, CONDENSER, CAPILLARY TUBE AND EVAPORATOR INFLUID COMMUNICATION, COMPRISING BIMETAL SWITCH MEANS OPERATIVELY CLOSEDIN RESPONSE TO THE TEMPERATURE OF THE EVAPORATOR OF THE REFRIGERATINGUNIT, A SOLENOID VALVE ASSEMBLY CONNECTED WITH SAID COMPRESSOR, A BYPASSCONDUIT CONNECTED AT ONE END THEREOF TO SAID SOLENOID VALVE ASSEMBLY ANDAT THE OTHER END THEREOF TO THE UPSTREAM SIDE OF THE EVAPORATOR; SAIDSOLENOID VALVE ASSEMBLY INCLUDING A SOLENOID COIL ASSOCIATED WITH SAIDBIMETAL SWITCH MEANS, AN ARMATURE ARRANGED IN SAID SOLENOID COIL ANDRECIPROCABLY MOVED BY SAID SOLENOID COIL, A NEEDLE ELEMENT CARRIED BYSAID ARMATURE FOR OPERATIVELY OPENING AND CLOSING SAID BYPASS CONDUIT,SAID SOLENOID VALVE ASSEMBLY BEING DESIGNED TO PRODUCE WHEN SAID BIMETALSWITCH MEANS IS CLOSED A MAGNETIC FORCE WITH AN INTENSITY INSUFFICIENTTO ACUTATE SAID ARMATURE AND SUFFICIENT TO HOLD THE ARMATURE IN ANACUTATED POSTION; AND SWITCH MEANS ASSOCIATED WITH SAID SOLENOID COILAND INDEPENDENTLY RENDERING SAID SOLENOID COIL OPERABLE TO PRODUCE ANADDITIONAL MAGNETIC FORCE SUFFICIENT TO ACTUATE THE ARMATURE IN SAIDSOLENOID COIL.